A Mesityl-Functionalized Double-Boron-Nitrogen-Oxygen-Embedded Multi-Resonance Framework Achieves Anti-Quenching Narrowband Deep-Blue Electroluminescence with EQE over 30% and CIEy of 0.046

Developing highly efficient deep-blue multi-resonance thermal activated delayed fluorescence (MR-TADF) materials for ultra-high-definition organic light-emitting diodes (OLEDs) displays that meet the stringent BT.2020 standard remains a significant challenge. In this study, we present a strategy to achieve high-performance deep-blue MR-TADF emitters by integrating a large π-conjugated double-boron-embedded MR skeleton with strategically positioned peripheral steric hinderance groups. The developed molecule, DMBNO, exhibits a narrow full-width at half maximum (FWHM) of 19 nm, with a deep-blue emission peak at 444 nm in diluted toluene solutions. Additionally, it achieves high photoluminescence quantum yield (PLQY) and a horizontal ratios of emitting dipole orientation (Θ//) exceeding 90% in doped films. Notably, DMBNO demonstrates anti-quenching properties and effectively suppresses spectrum broadening. Consequently, OLEDs based on DMBNO achieve a high maximum external quantum efficiency (EQEmax) of 32.3%, with an impressive Commission Internationale de l'Eclairage (CIE) y-coordinate of 0.046, fully satisfying the BT.2020 blue gamut at a high doping concentration of 10 wt%. These findings offer valuable insights into molecular design tactics for deep-blue MR-TADF emitters featuring high efficiency, ultra-pure color, and anti-quenching characteristics.